why haven't they found us and made contact yet?
What would they need to do to "make contact"? For instance, what if missiles were launched against them whenever they were detected in the atmosphere? What if they could cruise over Washington on two consecutive Saturday nights in full view of everybody and still be ignored because humans are fucking idiots?
Basically, even if they landed on the White House lawn and forced TV channels to cover it globally, there'd suddenly be an explosion or power cut, then endless news stories about a 'terrorist attack'. Those that acknowledged the blatant alien landing would be ridiculed as heretics. End of story and back to vacuous rumination over "are we alone?".
Where's that fucking comet - it's been 65 million years already...